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Old Mar 25th 2014, 06:08 AM   #1
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Question about efficiency=MA/IMA

A worker uses a pulley system to raise a 225-N carton 16.5 m. A force of 129 N is exerted and the rope is pulled 33.0 m.
a. What is the mechanical advantage of the pulley system.
b. What is the efficiency of the system.

In the Solution page it said that the MA=fe/fr =225 N/129 N=1.74 and the IMA=de/dr=33.0 m/16.5 m.

Can someone tell me what are the MA and IMA stand for?

Thanks.
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Old Mar 25th 2014, 06:46 AM   #2
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Of interest, perhaps?

Perhaps this is of interest. If not, sorry!

http://www.thermospokenhere.com/wp/0...awks_nest.html
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Old Mar 25th 2014, 06:49 AM   #3
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Originally Posted by THERMO Spoken Here View Post
Perhaps this is of interest. If not, sorry!

http://www.thermospokenhere.com/wp/0...awks_nest.html
Thank you all the same! I decide to ask my teacher tomorrow. I still can's understand it.
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Old Mar 25th 2014, 09:49 AM   #4
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MA = "mechanical advantage," and is a measure of force multiplication provided by the lifting mechansim, in this case the pulley system. It is equal to the ratio of the weight of the carton you are lifting to the force you apply on the rope to lift it. So here MA = 225/129 = 1.744, just as you figured it.

IMA = "Ideal Mechanical Advantage," and is the mechanical advantage yuo would have under ideal conditions, meaning no losses of power and efficiency = 100%. It's determined by the physical construct of the pulley system, in this case the ratio of the amount of rope you pull to the height the carton is lifted. So IMA = 33/16.5 = 2.

Note that the actual MA is less than ideal, so the efficiency of the mechanism is less than 100%. The ratio of MA/IMA gives the efficiency, which is 1.744/2 = 87.2%. Alternatively efficiency can be calculated from the ratio of the work done on the weight being lifted to the amount of work applied done by the person pulling the rope:

Eff = (225N x 16.5)/(129N x 33m) = 87.2%

Hope this helps.
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